Early and convenient detection has become extremely important against various diseases including cancers and infectious diseases. The earlier a disease is diagnosed, the more likely it can be cured or successfully managed. Although significant progress has been made in disease diagnosis and treatment, mortality rates of diseases such as AIDS and cancer have not changed in the last several decades. One possible reason is the lack of easy, fast, non-invasive and affordable screening tests for early disease detection. Capturing and identifying circulating tumor cells (CTCs) in human blood or body fluid samples, i.e. ‘liquid biopsy’ has gained a great deal of interest in recent years because of its potential for early and patient friendly cancer detection and monitoring. Antibody and other cell surface ligands have been widely used for cell separation via either magnetic-activated cell sorting (MACS) where ligands are immobilized to magnetic nanoparticles or flow cytometry in fluorescent-activated cell sorting (FACS) where antibodies are labeled with fluorescent dyes. Since flurorophore staining of antibody and immobilization of antibody to magnetic nanoparticles are expensive and time consuming, particularly for multiplexed cell separation, the parallelism and miniaturization inherent in microarray-based cell sorting methods were developed in recent years because they allow a wide variety of cell surface antigen groups to be screened simultaneously in a small area with low ligand and cell needs.
Cellular microarray assays have been used for profiling specific surface antigens expressed on living cancer cells such as leukemia, prostate cancer, antigen specific T cells and stem cells. However, their efficacy is often limited due to weak binding between the target cells and surface coated ligands and the inherent non-specific binding of non-targeted cells. In the aforementioned methods, a separate detection method is needed to analyze intracellular biomarkers of the captured cells. Usually the detection methods require cell lysis or fixing. Thus, there is a need of new detection methods which can identify cells alive so the captured target cells can be used for further analysis or treatment.